(a) Field of the Invention
The present invention relates to a circuit board for a display device and a display device having the circuit board.
(b) Description of the Related Art
Generally, a liquid crystal display includes two panels having pixel electrodes and a common electrode, and a liquid crystal layer having dielectric anisotropy which is interposed therebetween. The pixel electrodes are arranged in a matrix, are connected to switching elements such as thin film transistors (TFT), and are supplied with data voltages line by line. The common electrode is formed on the entire surface of one display panel and is supplied with a common voltage. Each pixel electrode, the common electrode, and the liquid crystal layer therebetween constitute a liquid crystal capacitor from the view point of circuitry. The liquid crystal capacitor forms a basic unit of a pixel together with the switching element connected to the liquid crystal capacitor.
The liquid crystal display displays images by applying a voltage to the two electrodes to generate an electric field in the liquid crystal layer and adjusting the intensity of the electric field to control transmittance of light passing through the liquid crystal layer. In order to prevent deterioration resulting from application of a constant electric field to the liquid crystal layer over a long time, the polarity of the data voltages with respect to the common voltage is inverted in the unit of a frame, a line, or a dot, or the common voltage and the data voltages are all inverted.
Among such liquid crystal displays, a middle-sized or small-sized liquid crystal display used specifically in mobile phones includes a liquid crystal panel assembly, a flexible printed circuit board (FPC) having signal lines for supplying input signals from the outside, and an integration chip for controlling them.
The liquid crystal display includes a display panel having pixels including switching elements and display signal lines, a gate driver for supplying a gate-on voltage and a gate-off voltage to gate lines among the display signal lines to turn the switching elements of the pixels on or off, and a data driver for supplying data voltages to data lines among the display signal lines and applying the data voltages to the pixels through the turned-on switching elements. The integration chip includes the gate driver or the data driver, or both, and is generally mounted on the display panel in the form of COG (Chip On Glass).
The signal lines are connected to the integration chip, and the integration chip processes signals from the outside and supplies the signals to the liquid crystal panel assembly. The integration chip generates drive power for driving the gate driver and the data driver described above, and supplies the drive power to the gate driver and the data driver. A power supply chip constructed in the form of an integrated circuit to generate the source power is built into the integration chip. Passive elements such as capacitors and resistors are required for generating the source power. Such passive elements are often disposed on the FPC without being built into the integration chip in consideration of the sizes of the passive elements, and are connected to the power source chip through power supply lines.
In order to prevent the signal lines and the power supply lines connected to the passive elements from directly intersecting each other, the FPC has a two-layered structure of a top side and a bottom side. That is, one of the signal lines and the power supply lines is drawn through the FPC via holes at the intersections therebetween.
The FPC having the two-layered structure causes an increase in manufacturing cost. In addition, even when the lines intersect each other on the top side and the bottom side without directly intersecting each other at the same side, noise occurs in signals due to parasitic capacitance resulting from the intersections.